Liver regeneration is a unique repair response to tissue damage where normally quiescent liver cells reenter the cell cycle and undergo cell division, regaining the damaged or lost tissue, while maintaining the differentiated function of the cells. Acute or chronic ethanol treatment impairs liver regeneration by mechanisms that remain poorly characterized. Deregulation of the liver's normal repair function may contribute to the development of alcoholic liver disease. The long-term objective of these studies is to characterize intracellular signaling events associated with liver regeneration and to assess how these signaling processes are affected by chronic ethanol treatment. In our previous studies we have characterized changes in energy metabolism of the liver during the onset of liver regeneration after partial hepatectomy (PHx). We have started to identify signaling mechanisms that link metabolic stress with the initiation of the regenerative response in the earliest time domain of liver regeneration, seconds to minutes after PHx. First, we will investigate how the early changes in energy state of the liver relate to upstream signals mediated by nitric oxide synthase (NOS) and a1-adrenergic agonists, using pharmacological tools and by suppressing NOS isoforms with short interfering RNAs transfected into the liver using viral vectors. Second, we will analyze how these early signals impact on the activation of growth factors and release of cytokines that are thought to initiate the transition of quiescent cells into the cell cycle and the subsequent mitogenic response. Third, we will address the question of the role of these signals in the initiation of mitochondrial biogenesis and the recovery of mitochondrial energy metabolism. We hypothesize that inadequate energy metabolism and its associated signaling pathways in the liver following chronic ethanol intake may contribute to defective liver regeneration. We expect that a better understanding of these early signaling events may lead to the development of rational therapies for ethanol-induced liver damage [unreadable] [unreadable]